1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to radio frequency integrated circuits used within such wireless communication systems.
2. Description of the Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
As is also known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
Typically, the data modulation stage produces baseband signals to include a digital in-phase component and a digital quadrature component. The digital in-phase and quadrature components are converted to the analog domain using digital-to-analog converters (DAC). The analog in-phase component is then mixed with an analog in-phase component of the local oscillation, while the Q component is mixed with a Q component of the local oscillation. The resulting mixed signals are then summed together to produce RF signals.
For direct conversion radios (those that convert directly from baseband to RF), if the I and Q processing circuitry of the data modulation stage are identically matched, the DACs are identically matched, and the elements of the mixers are identically matched, the resulting RF signals will be free from errors associated with mixing signals, which is generally referred to as local oscillation (LO) leakage. In practice, however, local oscillation leakage is produced because ideal matching of circuits and components thereof is not achievable. To minimize the effects of local oscillation leakage, direct conversion transmitters include local oscillation leakage compensation circuitry, which compensates for the mismatches of the DACs, and/or of the mixers.
An issue with local oscillation leakage compensation circuits is determining an appropriate setting. This issue arises in most, if not all, direct conversion radios because such radios include other compensation circuitry to correct for DC offset, frequency offsets, et cetera. When these other compensation circuits are active, they mask the LO leakage without compensating for it, thus making it difficult to obtain an accurate measure of LO leakage. Without an accurate measure of LO leakage, accurate compensation thereof is difficult.
Therefore, a need exists for a method and apparatus that accurately measures LO leakage within radio frequency integrated circuits and accurately compensates therefore.